When a heavily intoxicated 16-year-old girl was taunted, raped and possibly urinated on during an out-of-control night of high school drinking in Steubenville, Ohio, last summer, dozens of other teens had the chance to intervene as she was carried to at least three different house parties. Instead, some took pictures and posted them online, while others turned away as the victim was dragged or carried, apparently unconscious, from one place to another.

As the trial of two high school football players accused of the rape approaches, it’s hard not to wonder about those who simply watched. Why didn’t anyone try to stop the assault, even by anonymously dialing 911? Why did the bystanders apparently egg on the bullying that escalated into rape, seeing the behavior as something to broadcast rather than conceal? And, perhaps more important, how can the inertia of inaction be broken?

Unfortunately, bystander inaction is so common that it has been an active area of social-psychology research since 1964, when Kitty Genovese, a 28-year-old New York woman, was stabbed to death on the street in front of witnesses who failed to get help. The original version of the story — that 38 people saw the crime and did nothing — was later found to be inaccurate, with more people calling the police than was initially reported. But cases like Steubenville incident illustrate that bystander inaction persists, especially among teens and young adults. Research now suggests, however, that mobilizing witnesses is not only possible but could be an effective way to prevent these types of crimes from occurring or escalating.

Hundreds of colleges now offer programs to encourage intervention. “It’s just emerging,” says Sarah McMahon, associate director of the Center on Violence Against Women and Children at Rutgers University, of these efforts. “There are a number of programs now around the country, and the idea is very appealing. So far, the evaluations show that the programs do have a really positive effect both on willingness to step in and on actual behaviors.”

The interventions are based on research that suggests that the strongest enabling factor in sexual violence is the idea that such behavior is covertly condoned. “We know that people — especially adolescents — listen to peers,” says McMahon. “If their peers are expressing disapproval of the behavior, that’s really powerful, and that’s a key ingredient in how to ultimately prevent these crimes from happening, more than any other techniques that have been tried.”

In fact, studies show that teens’ beliefs about other people’s perspectives on the acceptability of bullying and sexual assault have a greater influence on their behavior than their own personal views. “Especially with men and boys, their willingness to intervene is based on whether or not they think their male peers would approve. That is the strongest factor, more so than their own attitudes,” McMahon says.

This means that even apparently minor expressions of sexism or jokes about rape — like those made by a former Steubenville student in a now infamous video — can have an outsize influence, because they imply that degrading women is acceptable and that rape is a laughing matter. By implicitly conveying such warped social norms, these “microassaults” discourage bystanders from standing up because they suggest that they won’t be supported in their attempts at deterrence and may even become targets themselves because their views stand out from the crowd’s.

Beliefs in myths about rape also predict inaction: for example, the idea that rape is always visibly violent and does not occur in situations where a person is simply incapable of consent, like severe intoxication. In court testimony, one of the Stuebenville bystanders justified his inaction by adhering to this myth, saying that he didn’t try to stop the football players from exposing the girl’s breasts because “at the time, no one really saw it as being forceful.”

Research shows that if just one person speaks up, that can break the sense of unspoken assent from bystanders that, for example, allows bullying to escalate into more severe forms of violence. Teaching bystanders to take responsibility — and to not simply assume that someone else will do something — is also important.

But breaking through these barriers to interrupt inappropriate behavior isn’t easy in these cultures: adolescents and young adults are often afraid to challenge their peers, especially if the perpetrators are perceived as having high social status. And in situations where underage drinking or drug use is occurring, teens often avoid notifying adults for fear of getting in trouble with their parents or risking college eligibility.

“The key is to try to shift those social norms,” says McMahon. “Lots of men and boys don’t approve, but they think others do, and so we need to find ways that they can express their real opinions.” Programs to encourage bystander action do just that, and McMahon is evaluating one such program in place at Rutgers University. It empowers students to speak up and establish that rape jokes and actual sexual violence should not be quietly tolerated and helps them consider in advance what to do in risky situations, as when an obviously incapacitated woman is being led into a private space where she might be harmed.

Data from that program may lead to useful information about how best to overcome social barriers and the fear linked to intervening when people witness sex crimes. “This is something we need to better understand so we can help people develop skills and know that there are many options when they face these situations,” McMahon says.